1. Field of the Invention
This invention relates to novel personal product compositions as well as to phosphate ester surfactants used in the compositions and methods for the preparation of these surfactants. A portion of the surfactant molecule used in the compositions of the invention functions as a so-called "benefit reagent" which will form when the molecule is metabolized by enzymes present in the body or elsewhere or which will form when the molecule spontaneously hydrolyzed on the skin surface. Personal product compositions comprising these phosphate esters include hair/body shampoos, cleansing creams, conditioners, cosmetic compositions, dental compositions, underarm deodorant/antiperspirant compositions and sunblock compositions. This list is not intended to be exhaustive and other compositions in which the surfactants may be used are also contemplated.
2. Prior Art
In the past decades, "mildness" has become an increasingly important criterion in selecting surfactants for personal products. The term "mildness" means that surfactants do not produce any skin irritation. Many consumers recognize the skin damaging effects surfactants may have. Therefore, a surfactant used for personal products should not only possess good surface active properties, but should also be safe on human skin.
Although many factors, e.g., removal of skin lipids, loss of naturally occurring hygroscopic materials in the stratum corneum, adsorption, protein denaturation, epidermal liposomal injury, are known to have an influence on skin irritation, it is generally believed that surfactants cause skin irritation by penetrating the stratum corneum and reacting with the inner cells of the epidermis. Accordingly, one approach to achieving "mildness" is to prevent surfactants from penetrating the stratum corneum and reacting with those cells.
A second approach for obtaining "mildness" is to design surfactants which can penetrate the stratum corneum but which, once they have penetrated, degrade to harmless components, possibly with the aid of enzymes. This second approach (the approach followed by the subject invention) attempts to take advantage of the enzymatic activity which is believed to be present in the sublayer of the stratum corneum. See Foster et al, Arch Derm.Res., 25:23-28 (1975) and Kermici et al, J. Soc. Cosmet Chem., 28:151-164 (1977).
It is also known in the art that hydroxy acids have beneficial effects on the skin. U.S. Pat. No. 4,197,316 to Yu et al. for example, discloses a non-irritating therapeutic composition for alleviating dry skin symptoms wherein the composition contains hydroxy acids (e.g., .alpha.-hydroxy, butyric acid, maleic acid and citric acid). U.S. Pat. No. 4,294,852 to Wildnaer et al. teaches skin treating compositions comprising hydroxy acids.
Accordingly, it would be particularly beneficial to design compositions comprising a surfactant molecule wherein the surfactant not only breaks down inside the skin or which spontaneously hydrolyzes upon contact with the skin surface, but to design a molecule which, once it has been broken down or once it has hydrolyzed, will have a beneficial effect on (e.g., alleviating dryness, imparting antimicrobial activity etc.) or deliver a benefit to the skin.
Monoalkyl phosphates (MAP) are known to have a very low irritancy potential and to possess good surface active properties when compared with typical anionic surfactants. Imokawa et al., J. Am. Oil Chem. Soc., 55:839 (1978). In addition to the mildness of MAP, mutagenicity, acute toxicity, and sub-acute toxicity tests have confirmed that MAPs are very safe. Imokawa, Fragrance Journal. 68:21-28 (1984). MAPs have also proved negative to skin allergy tests. These molecules thus would appear to be a good starting place in which to form molecules (for use in personal product compositions) which break down on the skin (or hydrolyze on the skin surface) and which might also provide a beneficial effect (such a produced by hydroxy acid) upon being broken down or hydrolyzing.
U.S. Pat. No. 4,350,645 to Kurosaki et al. describes a method for producing a phosphoric monoester. According to this disclosure, the monoester is formed from the reaction of phosphoric acid, P.sub.2 O.sub.5 and an organic hydroxy compound, ROH. The organic hydroxy compound used may be a saturated or unsaturated aliphatic alcohol, an alkylene oxide addition product of said aliphatic alcohol or an alkylphenol. Since the R group on the alcohol is not an acid, the monoester formed cannot contain an acid component. Accordingly, it follows that when the molecule is broken down or hydrolyzed, it could not form a hydroxy acid, a hydroxy carboxylic ester or a phosphocarboxy acid such as is hypothesized the molecule of the invention would. There is also no recognition of the importance the R group might have in the final compound. In addition, since this is a process patent, there is no teaching or suggestion of the use of the compounds in personal product compositions.
U.S. Pat. No. 4,736,051 to Wakatsuki et al. teaches a method for the preparation of an alkali metal salt of a diester phosphoric acid. On page 4, lines 38-42 is disclosed a generic formula IV which is similar to the compounds used in the compositions of the invention.
If b is defined as 1 in Formula IV such than an ester group is present, it can be seen that the single bonded ester oxygen is closer to the phosphorus moiety then the double bonded carboxyl oxygen. This is a critical distinction because hydrolysis of the ester group could yield only a phosphohydroxy group and not a phosphocarboxy group (since the carbonyl oxygen will have been cleaved off by hydrolysis). If b is defined as 0, then the compound differs from that of the subject invention because, since Y can only be hydrogen, a hydroxy group or an alkyl or alkenyl group, no ester is formed at all.
Finally, this patent is concerned with a method of forming the alkali metal salt or diester of phosphoric acid and so there is no appreciation that the use of specific compounds might have surprisingly advantageous effects when used in specific compositions. In particular, there is no teaching of these compounds in personal product compositions.
French Patent No. 4,118M to Kirsch discloses a molecule which is also similar in structure to one used in the compositions of the invention. This reference however, appears to be concerned with pharmaceutically active materials and not with personal product formulations.
Thus it would be useful to provide novel a molecule containing a portion which contains a salt (i.e., at least a partial salt) of the phosphate group in one portion of the molecule and an ester group in the other portion such that a hydroxy acid may form when the molecule is metabolized by enzymes in the skin or hydrolyzed upon contact with the skin.